Hypothetical mechanisms of a virus-versus-leukemia effect. The myeloid reservoir of latent CMV virus includes AML blasts that reactivate after SCT. (1) CMV-specific CTLs kill CMV antigen presented by leukemia; (2) CMV up-regulates LFA-1 in leukemia, increasing susceptibility to NK killing; (3) direct cytotoxic effect of CMV on AML cells.